The present invention relates to a method for obtaining three-dimensional images of anatomical structures by reconstruction of two-dimensional X-Ray fluorograms.
X-ray imaging is widely used to image internal organs for diagnostic purposes and to assist health practitioners during therapeutic interventions. In particular, this technique has found many applications in cardiology. For example, many intraventricular interventional cardiac procedures such as Direct Myocardial Revascularization and electro physiological mapping and ablation are conducted under X-ray fluoroscopy.
X-ray fluorograms are two-dimensional projections of anatomical structures. While these images provide useful information they do not allow the resolution of the three-dimensional shape of these structures. Cardiologists typically overcome the deficiencies of the fluorograms by combining the 2-D information of X-ray fluorograms with their knowledge of anatomy to perform (therapeutics) cardiac procedures. This method has the disadvantage of relying heavily of the experience and knowledge of the practitioner.
Three-dimensional X-ray images of internal organs can be obtained using X-ray computed tomography. In this technique, a large number of projections is obtained from different angles and using image reconstruction techniques it is possible to reconstruct the image of an organ. This technique however requires long acquisition times and is not compatible with therapeutic interventions requiring xe2x80x9creal timexe2x80x9d information about the position of surgical instruments within an organ for example.
Bi-plane X-ray fluorograms can be used to determine the 3-D position of individual points such as the tip of a catheter. By obtaining several 3-D position of a catheter it is possible to produce a 3-D map of an organ such as a ventricle for example. However, this technique requires the use of an additional tool (the catheter) and furthermore the resulting map is not integrated with the fluorogram. Bi-plane fluorograms have also been used to derive 3-D images without the use of positional indicators as described in U.S. Pat. No. 4,672,651. This document describes an image reconstruction method based on a relaxative correction algorithm of projections-backprojections that requires extensive image processing.
The instant invention overcomes the limitations of the prior art by providing a method for rapidly reconstructing the three dimensional image of an object using a single plane two dimensional X-ray projection image.
In one aspect of this invention there is provided a method for reconstructing the three dimensional (3-D) image of an object, symmetric about at least one plane, from a single two dimensional (2-D) X-ray projection image.
According to the method, an X-ray projection image is obtained with X-ray contrast agent filling the object. In this image, the intensity of each pixel (x,y) represents the X-ray absorbance of the contrast agent within the object. From this absorbance value, the distance travelled by the X-ray within the object can be calculated and the 3 dimensional image of the object reconstructed.
The invention thus relates to a method for the three dimensional image reconstruction of single plane 2-dimensional X-ray image projection of an object having at least one plane of symmetry comprising: substantially uniformly filling the object with an X-ray contrast agent said contrast agent having a pre-selected concentration and absorption coefficient; irradiating said contrast agent-filled object with X-rays substantially perpendicular to said at least one plane of symmetry of the object;detecting said X-rays transmitted through said contrast agent-filled object to define a 2-dimensional projection image with pixels (x,y) having an intensity related to the absorbance of said contrast agent-filled object; processing said 2-dimensional projection image to reconstruct the 3-dimensional image of said object, said processing including determining a distance D(x,y) travelled by said X-rays in the contrast agent-filled object by dividing the absorbance corresponding to the intensity of each pixel (x,y) by the concentration of the contrast agent within said object and multiplying the result thus obtained by the absorption coefficient of said contrast agent; dividing said distance D(x,y) by 2 to define a (+z) coordinate (equals to +D(x,y)/2) and a (xe2x88x92z) coordinate (equals to xe2x88x92D(x,y)/2) for each pixel (x,y); such that for each pixel (x,y) there is:
1) a (+z) coordinate=+D(x,y)/2 and
2) a (xe2x88x92z) coordinate=xe2x88x92D(x,y)/2;
and using the x,y,z coordinates thus determined to reconstruct the 3 dimensional image in a 3-dimensional axis system in which the x-y plane is parallel to the plane of symmetry of said object;
In a further embodiment, X-ray projection images are obtained with and without X-ray contrast agent filling the object (called the mask and live images respectively) and the mask image is subtracted from the corresponding live image. In the resulting final 2-dimensional projection image, each pixel (x,y) represents the X-ray absorbance of the contrast agent within the object. From this absorbance value, the distance travelled by the X-ray within the object can be calculated and the 3 dimensional image of the object reconstructed.
The invention thus also relates to a method for the three dimensional image reconstruction of single plane 2-dimensional X-ray image projection of an object having at least one plane of symmetry comprising:irradiating said object with X-rays substantially perpendicular to said at least one plane of symmetry of the object; detecting said X-rays transmitted through said object to define a 2-dimensional projection mask image with pixels (x,y) having an intensity related to the absorbance of said object; substantially uniformly filling the object with an X-ray contrast agent said contrast agent having a pre-selected concentration and absorption coefficient; irradiating said contrast agent-filled object with X-rays substantially perpendicular to said at least one plane of symmetry of the object; detecting said X-rays transmitted through said contrast agent-filled object to define a 2-dimensional projection live image with pixels (x,y) having an intensity related to the absorbance of said contrast agent-filled object; subtracting said mask image from said live image to obtain a 2-dimensional final image; processing said 2-dimensional final image to reconstruct the 3-dimensional image of said object, said processing including determining a distance D(x,y) travelled by said X-rays in the contrast agent-filled object by dividing the absorbance corresponding to the intensity of each pixel (x,y) by the concentration of the contrast agent within said object and multiplying the result thus obtained by the absorption coefficient of said contrast agent; dividing said distance D(x,y) by 2 to define a (+z) coordinate (equals to +D(x,y)/2) and a (xe2x88x92z) coordinate (equals to xe2x88x92D(x,y)/2) for each pixel (x,y); such that for each pixel (x,y) there is:
1) a (+z) coordinate=+D(x,y)/2 and
2) a (xe2x88x92z) coordinate=xe2x88x92D(x,y)/2;
and using the x,y,z coordinates thus determined to reconstruct the 3-dimensional image in a 3-dimensional axis system in which the x-y plane is parallel to the plane of symmetry of said object;